Re: [HACKERS] Block level parallel vacuum - Mailing list pgsql-hackers

On Tue, Nov 12, 2019 at 3:39 PM Masahiko Sawada
<masahiko.sawada@2ndquadrant.com> wrote:
>
> On Tue, 12 Nov 2019 at 18:26, Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >
> > On Tue, Nov 12, 2019 at 2:25 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> > > Yeah, maybe something like amparallelvacuumoptions.  The options can be:
> > >
> > > VACUUM_OPTION_NO_PARALLEL   0 # vacuum (neither bulkdelete nor
> > > vacuumcleanup) can't be performed in parallel
> > > VACUUM_OPTION_NO_PARALLEL_CLEANUP  1 # vacuumcleanup cannot be
> > > performed in parallel (hash index will set this flag)
> >
> > Maybe we don't want this option?  because if 3 or 4 is not set then we
> > will not do the cleanup in parallel right?
> >

Yeah, but it is better to be explicit about this.

> > > VACUUM_OPTION_PARALLEL_BULKDEL   2 # bulkdelete can be done in
> > > parallel (Indexes nbtree, hash, gin, gist, spgist, bloom will set this
> > > flag)
> > > VACUUM_OPTION_PARALLEL_COND_CLEANUP  3 # vacuumcleanup can be done in
> > > parallel if bulkdelete is not performed (Indexes nbtree, brin, hash,
> > > gin, gist, spgist, bloom will set this flag)
> > > VACUUM_OPTION_PARALLEL_CLEANUP  4 # vacuumcleanup can be done in
> > > parallel even if bulkdelete is already performed (Indexes gin, brin,
> > > and bloom will set this flag)
> > >
> > > Does something like this make sense?
>
> 3 and 4 confused me because 4 also looks conditional. How about having
> two flags instead: one for doing parallel cleanup when not performed
> yet (VACUUM_OPTION_PARALLEL_COND_CLEANUP) and another one for doing
> always parallel cleanup (VACUUM_OPTION_PARALLEL_CLEANUP)?
>

Hmm, this is exactly what I intend to say with 3 and 4.  I am not sure
what makes you think 4 is conditional.

> That way, we
> can have flags as follows and index AM chooses two flags, one from the
> first two flags for bulk deletion and another from next three flags
> for cleanup.
>
> VACUUM_OPTION_PARALLEL_NO_BULKDEL 1 << 0
> VACUUM_OPTION_PARALLEL_BULKDEL 1 << 1
> VACUUM_OPTION_PARALLEL_NO_CLEANUP 1 << 2
> VACUUM_OPTION_PARALLEL_COND_CLEANUP 1 << 3
> VACUUM_OPTION_PARALLEL_CLEANUP 1 << 4
>

This also looks reasonable, but if there is an index that doesn't want
to support a parallel vacuum, it needs to set multiple flags.

> > Yeah, something like that seems better to me.
> >
> > > If we all agree on this, then I
> > > think we can summarize the part of the discussion related to this API
> > > and get feedback from a broader audience.
> >
> > Make sense.
>
> +1
>

Okay, then I will write a separate email for this topic.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com